go-git: Improper single-quote escaping in go-git SSH transport

Impact

go-git's SSH transport constructs the remote exec command by wrapping the repository path in single quotes without escaping single quotes embedded inside the path. This diverges from canonical Git, which shell-quotes the path through sq_quote_buf so that an embedded ' becomes the '\'' close-escape-reopen sequence and the whole path round-trips as a single quoted argument.

A repository path containing a single quote can therefore break out of the quoted region in the exec command and be appended as additional shell tokens. On SSH servers that evaluate the exec command through a shell (for example a user account whose login shell is /bin/sh or /bin/bash, or a ForceCommand wrapper that re-evaluates $SSH_ORIGINAL_COMMAND), those additional tokens execute in that account's command-execution context. SSH servers that tokenize the exec command without shell evaluation, including the canonical git-shell setup, are not affected.

The vulnerable behaviour is on the SSH server side, not in go-git: the same bytes can be produced by any SSH client. The change in go-git is defense-in-depth that restores parity with canonical Git's wire format and prevents go-git from being a vehicle for reaching shell-evaluating servers through attacker-influenced repository paths.

Patches

Users should upgrade to a patched version in order to mitigate this issue. The fix ports sq_quote_buf from canonical Git into go-git's SSH transport so that the wire output is byte-identical to what git itself would send for the same input.

Versions prior to v5 are likely to be affected, users are recommended to upgrade to a supported go-git version.

Credit

Thanks to @N0zoM1z0 for reporting this to the go-git project. :bow: